Systems and arrangements to interconnect components of a semiconductor device

ABSTRACT

Systems and arrangements to interconnect cells and structures within cells of an integrated circuit to enhance cell density are disclosed. Embodiments comprise an adjusted polysilicon gate pitch to metal wire pitch relationship to improve area scalars while increasing ACLV tolerance with a fixed polysilicon gate pitch. In some embodiments, the wire pitch for at least one metallization layer is adjusted to match the pitch for the polysilicon gate. In one embodiment, the next to the lowest metallization layer running in the same orientation as the polysilicon gate, utilized to access the input or output of the interconnected cell structures is relaxed to match the minimum contacted gate pitch and the metal is aligned above each polysilicon gate. In another embodiment, the polysilicon gate pitch may be relaxed to attain a smaller lowest common multiple with the wire pitch for an integrated circuit to reduce the minimum step off.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application that claims benefit of theearlier filing date of U.S. patent application Ser. No. 11/167,752,entitled “SYSTEMS AND ARRANGEMENTS TO INTERCONNECT COMPONENTS OF ASEMICONDUCTOR DEVICE”, filed on Jun. 27, 2005 now U.S. Pat. No.7,492,013.

FIELD

The present invention generally relates to the field of integratedcircuits. More particularly, the present invention relates to systemsand arrangements to interconnect cells and structures within cellsformed in a substrate of an integrated circuit to enhance cell densityand improve the across chip line variance (ACLV) tolerance for theintegrated circuit.

BACKGROUND

Typical integrated circuit designs incorporate several metallizationlayers on top of a substrate to interconnect structures of cells formedin the substrate. In current designs, cells typically includecomplimentary metal oxide semiconductor (CMOS) circuits. CMOS circuitsinclude p-type metal oxide semiconductor (PMOS) and n-type metal oxidesemiconductor (NMOS) transistors formed from diffused areas of siliconand polycrystalline silicon, often referred to as polysilicon. Thepolysilicon areas are formed on top of a gate oxide above the diffusedareas to form gates. The polysilicon areas also couple with the diffusedareas on opposing sides of the gate to form electrodes for the sourceand drain of the transistors. Formation of the metallization layers overthe substrate facilitates interconnection of the transistors to formmore complex devices such as NAND gates, inverters, and the like.

The metallization layers utilize lines and vias to interconnect thetransistors in each of the cells as well as to interconnect the cells toform the integrated circuit such as a processor, state machine, ormemory. Lines typically reside in parallel paths within each layer.Lines in adjacent layers often run perpendicular to one another althoughlines in adjacent layers are separated by a non-conductive passivationlayer also referred to as an inter-level dielectric layer such as, e.g.,silicon oxide. The silicon oxide is etched to form the vias, whichinterconnect the lines of various metallization layers in accordancewith the circuit design. Inputs and outputs of the integrated circuitare brought to a surface with vias to bond the circuits with pins of achip package. The chip package typically includes an epoxy or ceramicthat encloses the integrated circuit to protect the circuit from damageand pins to facilitate a connection between the inputs and outputs ofthe integrated circuit and, e.g., a printed circuit board.

As generations of integrated circuits are scaled down to increasefunctionality and speed available in a chip package, designers mustcontinually scale down cell structures to smaller and smaller dimensionsto increase the density of cells per area of the substrate. In fact, thescaling theory has predicted that processor sizes will decrease by halfin each generation so a 50% area scalar is a goal when designing a newsmaller technology generation of integrated circuits. Further, to takeadvantage of the smaller cells, the lines must be formed at smallerpitches.

In recent technology generations, numerous design constraints and ruleshave been developed that bound the patterns of cells in an integratedcircuit. The rules and constraints take into consideration margins oferror in locating the cells in the substrate, ways to reduce themagnitude of leakage, as well as many other considerations to assure theperformance of the resulting integrated circuit. Rules delineate minimumdistances between structures of cells, lines, vias, and the like. Metaldirection relative to the gate material, metal layer chosen for powerdistribution within the cell, cell height, metal pitch, etc., are allconstraints of a chosen pattern or physical layout of the cells. Forexample, one critical constraint is related to the width of thepolysilicon gate material. The width of polysilicon gate materialdefines the length of the channel of a device. Longer channels add moredelay to the response of a device, which is sometimes desirable. Manycurrent designs, however, interconnect two or more short channel devicesin series to create long channel devices thus reducing hardshipsinvolved with building long channel devices into the integratedcircuits.

Another critical constraint is the metal pitch. Metal pitch determinesthe accessibility of cells so metal pitch directly impacts the celldensity of the integrated circuit. Further, the length ofinterconnections between cells impacts the performance. For instance,longer lines have increased resistance, increasing heat dissipation inthe integrated circuit. Longer lines also increase the capacitance ofthe overall design. Thus, while the first metallization layer istypically set to the tightest wire pitch, all remaining metallizationlayers of common thickness are constrained to a constant minimum metalpitch that facilitates interconnection of the cells. Current integratedcircuits typically have six to eight metallization layers.

To meet such design rules and constraints and to maximize cell density,one semi-custom design technique involves creating a standard library ofcells. The cell heights and widths are constrained to integrals of astandard grid so cells may be placed next to each other horizontally andvertically within the grid without violating the rules and constraintsfor the integrated circuit. The standard grid is an integral of thewiring pitch. Further, the cells are constrained to a constant cellheight but the width of each cell may vary to accommodate various cellconfigurations while maximizing cell density for any combination ofcells utilized to build the integrated circuit.

In most cases, the technology minimum ground rules are generally used todefine each cell's physical architecture and minimizing the cell widthfor a particular cell improves the cell density for the integratedcircuit. In the past, the polysilicon, or device gate material, was notrequired to be on a standard or single pitch (width plus space) so thewidth of the cells could be minimized by placing the polysiliconanywhere such that the minimum polysilicon width plus space was notviolated. The minimum space in this context, is the space required tocontact a diffusion area with a via/contact between the polysiliconareas.

As technology features grow ever smaller, the ability to process likedrawn objects of the same width within a tight tolerance across the chiphas become very difficult. This across chip line variance (ACLV)effectively determines the fastest and leakiest devices as well as theslowest devices. Because the designer must address both worst-case andbest-case extremes in performance and must also take into account theever-increasing leakage current associated with very short channeldevices, ACLV is receiving increased focus. One way to improve ACLV isto force all polysilicon to be the same width (device or channel length)and for it to be positioned at a common, fixed pitch.

While forcing the polysilicon to be at a fixed pitch improves the ACLV,the cell density is degraded. For instance, when considering developmentof a standard cell library, one such consideration is the cell wiringpitch. The cell height and width are generally defined as an integermultiple of the wiring pitch so every cell can be accessed via thewiring in the metallization layers. For purposes of the followingillustrations, consider metallization layer one, M1, runninghorizontally and metallization layer two, M2, running vertically(orthogonal to M1). In this manner, all lines on odd numberedmetallization layers run horizontally and all lines on even numberedmetallization layers run vertically. This orthogonal arrangement, whichis generally practiced, allows effective wiring. Accordingly, the widthof the cell (horizontal) is generally defined as an integer number of M2wiring tracks or pitches to allow any circuit to be placed next to anyother circuit along the x-axis. Similarly, the height of the cell is aninteger number of M1 tracks allowing any circuit to be placed next toany other circuit along the y-axis.

As a first illustration, consider the 90 nanometer (nm) technology andassume the polysilicon is running orthogonal to M1 and in parallel toM2, the M1 pitch is relaxed to match the larger M2 pitch, and the M2pitch is set to 0.28 micrometer (um). In one 90 nm technology, forinstance, the polysilicon gate pitch can be as short as 0.22 um with norequirement for the polysilicon to be positioned at a common, fixedpitch. Thus, the polysilicon gate pitch is smaller than the M2 pitch toallow gates to be placed wherever they produce the best cell density.Note, that the cell width must be a multiple of the 0.28 um M2 pitch toallow any circuit to be placed next to any other circuit on the x-axisas stated above. Hence, any inefficiency in the cell's layout can resultin an increase in cell width from n-tracks to n+1 tracks. Stated anotherway, if the cell layout misses terminating on the M2 wiring track gridby even one layout grid snap, which is typically 0.01 um, then the cellwidth must be increased to the next minimum step off, or offset, of 0.28um. This can invoke serious deficiencies in density.

The new design constraint for the 65 nm technology generation ofintegrated circuits that forces the polysilicon to be placed at a commonpitch, removes the ability to adjust the position of the polysilicon tominimize the width of a cell. Thus, to accommodate the standard celldesign, the minimum grid with respect to cell width is the least commonmultiple of the wiring pitch and the polysilicon gate pitch.

In the 65 nm technology, the wiring pitch in the metallization layers isreduced to, e.g., 0.20 um to maximize cell density with respect to theability to interconnect the smaller cells. Assume also, for example,that the polysilicon pitch is fixed at 0.25 um. Thus, the least commonmultiple of the metal pitch and the polysilicon pitch is 1.0 um or onemicron. In other words, the minimum cell width for this design is fivewiring tracks. If the cell design misses 1.0 um by 0.01 um (i.e., thecell width is 1.01 um), the next minimum step off is 2.0 um so the cellis ten wiring tracks wide instead of five wiring tracks wide. As aresult, a cell that utilizes six wiring tracks in the 90 nm technologymay utilize ten wiring tracks in the 65 nm technology due to the commonpitch requirement for the polysilicon, which is a 66% increase in thenumber of tracks consumed by the cell. Further, many cells in a standardcell library for the 65 nm technology can be designed with a cell widththat is smaller than five wiring tracks.

What is needed is a layout strategy for a standard cell design that isconsistent with this constant polysilicon pitch requirement to improveACLV while minimizing the impact of the constant polysilicon pitch oncell density.

SUMMARY

The problems identified above are in large part addressed by systems andarrangements to adjust resource accessibility based upon usage modes.One embodiment comprises a method to form an integrated circuitconstrained by a gate pitch. The method generally involves identifyingthe gate pitch, the gate pitch being a distance between a centerline ofa first gate and a centerline of a second gate that facilitatesplacement of a contact between the gates and in contact with a diffusionarea of a substrate; and forming a set of metallization layers over thesubstrate comprising lines, the lines being substantially parallel tothe gates, wherein at least one of the set is an adjusted metallizationlayer comprising adjusted lines, the adjusted lines being pitched at thegate pitch and substantially aligned with the gates.

Another embodiment comprises an integrated circuit constrained by a gatepitch. The integrated circuit may comprise a substrate comprising gatespitched at the gate pitch, the gate pitch being a distance between acenterline of a first gate and a centerline of a second gate of thegates that facilitates placement of a contact between the first gate andthe second gate to contact a diffusion area of a substrate; and a firstset of metallization layers formed over the substrate comprising lines,the lines being substantially parallel to the gates, wherein at leastone of the first set comprises an adjusted metallization layercomprising adjusted lines, the adjusted lines being substantiallyparallel to the gates, pitched at the gate pitch, and substantiallyaligned with the gates.

A further embodiment comprises an integrated circuit constrained by agate pitch. The integrated circuit may comprise a substrate comprisinggates pitched at the gate pitch, the gate pitch being greater than aminimum distance between a centerline of a first gate and a centerlineof a second gate of the gates that facilitates placement of a contactbetween the first gate and the second gate to contact with a diffusionarea of a substrate, wherein the gate pitch is adapted to have a commonmultiple with a wire pitch that is smaller than a lowest common multipleof the minimum distance and the wire pitch; and a set of metallizationlayers formed over the substrate comprising lines, the lines beingpitched at the wire pitch.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which, like references may indicate similarelements:

FIG. 1 depicts an embodiment of a system that incorporates an embeddedprocessor having a mixed grid arrangement for increased cell density;

FIGS. 2A-B depict an embodiment in a plane view and cross-section viewfor metallization layers two through four in a mixed grid arrangementsuch as the mixed grid arrangement for the embedded processor of FIG. 1;

FIGS. 3A-D depict an embodiment of a 65 nm technology CMOS cell for astandard library comprising an adjusted M2 wire pitch;

FIGS. 4A-B depict an embodiment of a 65 nm technology CMOS cell for astandard library comprising a relaxed polysilicon device pitch;

FIG. 5 illustrates a table indicating area scalars from a 90 nmtechnology to a 65 nM technology for CMOS cells having a standard gridarrangement and two alternative mixed grid arrangements;

FIG. 6 depicts a flowchart of an embodiment to form an integratedcircuit with an adjusted wire pitch; and

FIG. 7 depicts a flowchart of an embodiment to form an integratedcircuit with a relaxed polysilicon gate pitch.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of example embodiments of theinvention depicted in the accompanying drawings. The example embodimentsare in such detail as to clearly communicate the invention. However, theamount of detail offered is not intended to limit the anticipatedvariations of embodiments; but, on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present invention as defined by the appendedclaims. The detailed descriptions below are designed to make suchembodiments obvious to a person of ordinary skill in the art.

Generally speaking, systems and arrangements to interconnect cells andstructures within cells formed in a semiconductor substrate of anintegrated circuit to enhance cell density are disclosed. Embodimentscomprise an adjusted polysilicon gate pitch to metal wire pitchrelationship to improve area scalars while increasing ACLV tolerancewith a fixed polysilicon gate pitch. In some embodiments, the wire pitchfor at least one metallization layer is adjusted to match the pitch forthe polysilicon gate. In one embodiment, the lowest metallization layerrunning in the same orientation as the polysilicon gate, utilized toaccess the input or output of the interconnected cell structures isrelaxed to match the polysilicon gate pitch and the metal is alignedabove each polysilicon gate. For instance, if the second metallizationlayer (M2) is the lowest metal running in the same orientation as thepolysilicon gate, vias V1 may be utilized to interconnect metal-1 (M1)that is connected to the polysilicon gates by means of contacts withmetal lines of M2. Similarly, if the third metallization layer (M3) isthe lowest and in parallel with the polysilicon gate pitch, vias V2 maybe utilized to interconnect the polysilicon gates which are connected upto M2 with metal lines of M3.

In an alternative embodiment, the polysilicon gate pitch may be relaxedto attain a smaller lowest common multiple with the wire pitch for anintegrated circuit, advantageously reducing the minimum step off. Forexample, if the minimum polysilicon gate pitch is 0.25 um and theminimum wire pitch is 0.20 um for the integrated circuit, the lowestcommon multiple is 1.0 um, which is also the minimum step off.Embodiments may advantageously relax the polysilicon gate pitch to,e.g., 0.30 um, to offer a minimum step off of 0.60 um.

While portions of the following detailed discussion describe manyembodiments comprising employing a metallization layer two (M2) with anadjusted pitch, upon review of the teachings herein, a person ofordinary skill in the art will recognize that the pitch may be adjustedon a different metallization layers and, in some embodiments, on morethan one metallization layers. Further, embodiments discusspolycrystalline silicon gate structures, silicon substrates, metallines, and the like, but one of ordinary skill in the art will recognizethat other materials may substituted for these structures when employedin accordance with similar constraints to perform substantiallyequivalent functions.

Turning to the drawings, FIG. 1 illustrates an embodiment of aSystem-on-Chip (SoC) 100. SoC 100 may be a system on a chip with atleast one processing element, memory elements, I/O interfaces, and coresattached to a local bus or multiple on-chip buses. More specifically,SoC 100 comprises a mixed grid processing element such as a Mixed GridPowerPC 110, a local processor bus (PLB) 111, an on-chip peripheral bus(OPB) 140, and a number of supportive components, such as a synchronousrandom access memory (SRAM) 112, a double data rate (DDR) synchronousdynamic random access memory (SDRAM) controller 114, a PeripheralComponent Interconnect-Extended (PCI-X) bridge 116, a direct memoryaccess (DMA) 118 and a DMA controller 122, an Ethernet Medium AccessControl (MAC) protocol device 134 employed to provide the data linklayer for an Ethernet local area network (LAN) system, processor coretimers 130, an interrupt controller 132, and an OPB bridge 120interfacing with the OPB 140 and PLB 111.

As shown in FIG. 1, other devices provided for interfacing with the OPB140 include one or more of the following: a random access memory/readonly memory (RAM/ROM) Peripheral controller 144, an external bus master146, a Universal Asynchronous Receiver Transmitter (UART) device 148, anInter-IC bus (12C) interface 150, a general purpose I/O interface (GPIO)152, and a gateway interface (GPT) 154.

In further embodiments, the computational capabilities of SoC 100 may beenhanced, for, e.g., networking applications through the addition ofspecial-purpose processor cores (not shown) attached to the PLB 111,which operate in parallel with Mixed Grid Power PC 110. These additionalspecial-purpose processor cores may utilize small silicon areas byexclusion the features found in typical general-purpose processors(e.g., a memory management unit to support virtual addressing, etc.).

In other embodiments, Mixed Grid Power PC 110 is not limited to SoCdesigns, but could also be implemented in standard digital signalprocessors, micro-controllers, field programmable gate arrays,application specific integrated circuits, and microprocessors.

In the present embodiment, Mixed Grid Power PC 110 may be an embeddedprocessor such as IBM's PowerPC 440 or 405 processor core. Mixed GridPower PC 110 comprises a high cell density due to a mixed gridarrangement that adjusts a relationship between the device gate pitchand the wire pitch of at least one metallization layer. Morespecifically, in some embodiments, Mixed Grid Power PC 110 comprises anadjusted M2 metallization wire pitch. The adjusted wire pitch for M2 isequal to the polysilicon gate pitch and aligns the lines of M2 over thecenterlines of the polysilicon gates. Such embodiments advantageouslyreduce area scalars for cells such as the cells described in table 500of FIG. 5.

In further embodiments, Mixed Grid Power PC 110 comprises a relaxedpolysilicon gate pitch. The gate pitch is increased to 0.30 um to reducethe lowest common multiple with the minimum wire pitch from 1.0 um to0.60 um. Such embodiments also advantageously reduce area scalars forcells such as the cells described in table 500 of FIG. 5.

FIGS. 2A-B illustrate an embodiment in a plane view and cross-sectionview for metallization layers one (M1), two (M2), three (M3), and four(M4) in a mixed grid arrangement such as the mixed grid arrangementemployed in Mixed Grid Power PC 110 of FIG. 1. FIG. 2A-B depicts theplane and cross-section view of four metallization layers, M1, M2, M3,and M4 arranged with a relaxed or adjusted M2 wire pitch 215.Metallization layers, which are represented in FIG. 2A by M2 lines,M1/M3 lines, and M4 lines, generally form a grid to facilitate access tocells on a silicon substrate. The metal lines are formed along thedesignated pathways to interconnect structures of the cells and toconnect the cells with other cells to implement logic functions such asfunctions for, e.g., an arithmetic logic unit (ALU), an adder, afloating point unit (FPU), a pre-decoder, a cache controller, etc.

The lines of M2, M1/M3, and M4 in FIG. 2A represent valid pathwaysavailable for the lines of each of these layers, which are separatedfrom each other via non-conductive materials such as a silicon-oxide(SiO2). More specifically, once the cell structures are formed in thesilicon substrate, metallization layers are formed over the substrate.Passivation layers 235, as depicted in FIG. 2B, separate each of themetallization layers with non-conductive materials so lines shown inFIG. 2A do not contact one another at intersections unless a via isformed at the intersection.

After forming a passivation layer, a portion of the layer is typicallyetched away utilizing a photo-resist mask. The etching process removes adepth of the passivation layer at points along the pathways tofacilitate creation of the metal lines. Etching removes the entirepassivation layer at locations for vias such as intersections 230.Advantageously, the adjusted wire pitch 215 for M2 lines facilitatesplacement of vias in adjacent intersections 230 for improved V1redundancy and pin access. In particular, at one or more of locations230, poly contacts may interconnect M1 lines with polysilicon (notshown), vias V1 may interconnect M2 lines with M1 lines, and vias V2 mayinterconnect an M2 line with a higher layer line such as an M3 linewhile satisfying spacing restraints for vias. Further, the increasedflexibility in placement of vias and pin access may reduce the lengthsof wires interconnecting the cells and, as a result, may reduce thecapacitance associated with an integrated circuit such as Mixed GridPower PC 110 of FIG. 1. Reducing the capacitance can increaseperformance and decrease power consumption of the integrated circuit.

The M2 wire pitch 215 matches the minimum contacted device pitch, whichis also referred to as the minimum contacted gate pitch or poly pitch.As a result, M2 is arranged on a wider pitch than the minimum wire pitch210 and 220, which is the pitch indicated for M1 lines, M3 lines, and M4lines. Embodiments such as the embodiment in FIG. 2A may advantageouslyoffer improved area scaling for cells in a standard cell library. Forinstance, a NAND gate that is four tracks wide in 90 nm technology isfive wiring tracks wide in 65 nm technology when M2 lines are pitched ata minimum wire pitch of 0.20 um, which is a 0.63 area scalar. However,by adjusting the pitch of metallization layer M2 to match the fixed gatepitch of 0.25 um, the same NAND gate can be designed to be three trackswide, which is a 0.47 area scalar as is described in Table 500 of FIG. 5in the NAND2 row 560 at columns 515, 520, 525, and 530.

Looking now at FIG. 2B, there is shown an illustration of across-section of the metallization layers depicted in FIG. 2A. FIG. 2Bprovides an illustration of how metal lines of the metallization layersM1, M2, M3, and M4, may interconnect structures of a cell as well ascells with other cells of the integrated circuit. M2 layer 232 and M4layer 234 include lines along a pathway that is perpendicular to theplane of the figure, while the M1 layer 231 and M3 layer 233 includelines that run parallel to the plane of the figure. M2 layer 232includes lines defined on a constant wire pitch 215, which issubstantially equal to and aligned with the pitch of the polysilicongates (not shown). M1 layer 231, M3 layer 233, and M4 layer 234 includelines that are pitched at the minimum wire pitch 205, 220, and 210respectively.

FIG. 2B illustrates two separate interconnections. In the firstinterconnection, line 238 of M1 layer 231 connects with line 240 of M2layer 232 by means of via 239, via 241 connects line 240 of the M2 layer232 with line 242 of the M3 layer 233, and via 243 connects line 242with line 244 of M4 layer 234. In the second interconnection, line 248of M1 layer 231 connects with line 250 of M2 layer 232 by means of via249, via 251 connects line 250 of M2 layer 232 with line 252 of M3 layer233, and via 253 connects line 252 with line 254 of the M4 layer 234.Notice that vias 239 and 249 are located at adjacent M2 layer lines 240and 250. These vias 239 and 249 may be located at adjacent lines becausethe relaxed wire pitch of M2 layer 232 provides the minimum spacing forvias, which is inherent to the minimum contacted gate pitch. Theallowance of vias, of a same type, associated with two dissimilar netson two adjacent wiring tracks results in improved circuit pin access.This allowance also permits room for via redundancy to aid designintegrity.

Turning now to FIGS. 3A-B, there is shown an embodiment of a 65 nmtechnology CMOS inverter 300 comprising an adjusted M2 wire pitch of0.25 um for a standard cell library. In FIG. 3A, inverter 300 shows somemajor features of the cell while excluding other features for clarity.FIG. 3B depicts a circuit diagram to illustrate the features andinterconnections of inverter 300. Boundary 305 shows the extent ofinverter 300 which, in accordance with the constraints of thetechnology, may also be the boundaries of adjacent cells. Note thatpower contacts 315 and ground contacts 340 include contacts on boundary305 that are often referred to as power bumpers. These power bumpers maybe utilized by both inverter 300 and the adjacent cells.

Inverter 300 comprises PMOS transistors 301 and NMOS transistors 302interconnected to provide the functionality of an inverter. While PMOStransistors 301 and NMOS transistors 302 are illustrated as singletransistors, as can be seen in FIG. 3A, PMOS transistors 301 comprisetwo transistors in parallel and NMOS transistors 302 comprise twotransistors in parallel to increase the capacity of these transistors.The transistors 301 and 302 include polysilicon gates 310 pitched at aminimum contacted gate pitch of 0.25 um and diffusion areas 320 and 335.Note that floating polys 312 and 347 maintain the constant pitch for thepolysilicon to preserve the fixed poly pitch for ACLV but may bereferred to as “dummy polys” because they are not used to build thetransistors 301 and 302. As will be illustrated in FIG. 3C, a dual pfetand nfet comprising an inverter can be laid out in a smaller area(2-tracks wide rather than the illustrated 3-track wide rendition ofFIGS. 3A and B) using the same matched M2/polysilicon pitch.

M2 lines are pitched at 0.25 um and substantially aligned withcenterlines of all polysilicon including input poly 310 and 345 tofacilitate access input poly 310 and 345. As a result of the relaxedwire pitch of the M2 lines, the area scalar of inverter 300 is reducedwith respect to the area scalar offered by the minimum wire pitch of0.20 um. Table 500 of FIG. 5 describes these differences in columns 515,520, 525, and 530 on the inverter row 550. In many embodiments, the M2layer is the only metallization layer with this relaxed wire pitch andthe remainder of the metallization layers, with the exception ofpossibly the M1 layer, are set to the minimum wire pitch. For instance,notice that M3 and M4 have a pitch of 0.20 um. However, the M1 layer mayalso be relaxed to match the 0.20 um minimum wire pitch.

Input contacts 325 couples with the input poly 310 and 345, which may beinterconnected to all portions of the polysilicon. The input poly 310and 345 interconnects the gates of PMOS transistors 301 and NMOStransistors 302. With a sufficiently high voltage applied to inputcontacts 325, PMOS transistors 301 will turn off and NMOS transistors302 will turn on. On the other hand, when a sufficiently low voltage isapplied to input contacts 325, PMOS transistors 301 will turn on andNMOS transistors 302 will turn off.

The line width of the input poly 310 and 345 substantially determinesthe length of the channel of both PMOS transistors 301 and NMOStransistors 302. In the present embodiment, the pitch of the input poly310 and 345 defines the maximum channel length because the pitch is theminimum contacted gate pitch. In the embodiment illustrated in FIGS.4A-B, the input poly 410 and 445 is pitched at a relaxed pitch of 0.30um, which is larger than the minimum contacted gate pitch. Thus, theembodiment of FIGS. 4A-B advantageously offer the ability to design alonger channel device by increasing the width of the input poly 410 and445 while preserving a fixed poly pitch for ACLV.

Referring again to FIGS. 3A-B, output contacts 330 couple the drain ofPMOS transistors 301 and the drain of NMOS transistors 302 throughoutput M1 metal 306. The leftmost two power contacts 315 couple thesources of PMOS transistors 301 to a voltage source and the rightmosttwo ground contacts 340 couple the sources of NMOS transistors 302 witha low voltage source or ground. Input contacts 325 connect input M1metal 307 to input poly 310. For example, when PMOS transistors 301 areturned on and NMOS transistors 302 are turned off, PMOS transistors 301provide an electrical path from power contacts 315 to output contacts330 to pull up the voltage at output contacts 330 toward the voltage ofthe high voltage source. Similarly, when NMOS transistors 302 are turnedon and PMOS transistors 301 are turned off, NMOS transistors 302 providean electrical path to pull down the voltage at or discharge outputcontacts 330.

FIGS. 3C-D depict another embodiment of a 65 nm technology CMOS inverter350 still comprising the adjusted M2 wire pitch of 0.25 um for astandard cell library. In this realization, the inverter layout onlyrequires two M2 tracks, which results in an area scalar of 0.42. Table500 of FIG. 5 describes this inverter on row 555 in columns 525 and 530.When contrasted with the inverter layout illustrated in FIGS. 3A-B, thisrealization is significantly more area efficient. Table 500 of FIG. 5describes differences in columns 515, 520, 525, and 530 on the inverterrow 555.

Inverter 350 comprises PMOS transistors 351 and NMOS transistors 352interconnected to provide the functionality of an inverter. While PMOStransistors 351 and NMOS transistors 352 are illustrated as singletransistors, as can be seen in FIG. 3C, PMOS transistors 351 comprisetwo transistors in parallel and NMOS transistors 352 comprise twotransistors in parallel to increase the capacity of these transistors.The transistors 351 and 352 include polysilicon gates, or input poly360, pitched at a minimum contacted gate pitch of 0.25 um and diffusionareas 370 and 385. Note that in this realization no floating polys arenecessary to maintain the constant pitch for the polysilicon to preservethe fixed poly pitch for ACLV.

Output contacts 380 couple the drain of PMOS transistors 351 and thedrain of NMOS transistors 352 through output M1 metal 308. The two powercontacts 365 couple the sources of PMOS transistors 351 to a voltagesource and the two ground contacts 390 couple the sources of NMOStransistors 352 with a low voltage source or ground. Input contact 375connects input M1 metal 357 to input poly 360. For example, when PMOStransistors 351 are turned on and NMOS transistors 352 are turned off,PMOS transistors 351 provide an electrical path from power contacts 365to output contacts 380 to pull up the voltage at output contacts 380toward the voltage of the high voltage source. Similarly, when NMOStransistors 352 are turned on and PMOS transistors 351 are turned off,NMOS transistors 352 provide an electrical path to pull down the voltageat or discharge output contacts 380.

FIGS. 4A-B depict an embodiment of a 65 nm technology CMOS inverter 400comprising a relaxed polysilicon device pitch of 0.30 um for a standardcell library. Metallization layers have a minimum wire pitch of 0.20 um,advantageously offering a maximum wire density while the relaxed devicepitch facilitates an area scalar of 0.5 as described in column 540 ofinverter rows 550 and 555 in Table 500 of FIG. 5. Note that inverter 400is now three minimum pitch wire tracks wide and the relaxed device pitchadvantageously provides the opportunity for designers to build longerchannel devices with the extra space between polysilicon gates.

FIG. 4A shows some major features of inverter 400 while excluding otherfeatures for clarity. FIG. 4B depicts a circuit diagram to illustratethe features and interconnections of inverter 400. As in FIG. 4A,boundary 405 shows the extent of inverter 400 which, in accordance withthe constraints of the technology, may also be the boundaries ofadjacent cells. Note that power contacts 415 and ground contacts 440 areon boundary 405 and that these power bumpers may be utilized by bothinverter 400 and the adjacent cell.

Inverter 400 comprises a PMOS transistor 401 and a NMOS transistor 402interconnected to provide the functionality of an inverter. Thetransistors 401 and 402 include polysilicon gates, or input poly 410,and diffusion areas 420 and 435.

Input contact 425 couples with the input poly 410. The input poly 410interconnects the gates of PMOS transistor 401 and NMOS transistor 402and input contact 425 connects input poly 410 with input M1 metal 427.Output contacts 430 couple the drain of PMOS transistor 401 and thedrain of NMOS transistor 402 through output M1 metal 408. The powercontacts 415 couple the source of PMOS transistor 401 to a voltagesource and the ground contacts 440 couple the source of NMOS transistor402 with a low voltage source or ground. Otherwise, inverter 400operates in substantially the same manner as inverters 300 and 350.

FIG. 5 illustrates a table 500 indicating area scalars from a 90 nmtechnology to a 65 nm technology for CMOS cells having a standard gridarrangement and two alternative mixed grid arrangements. Column 505lists common cells for integrated circuits. In particular, column 505lists two inverters in rows 550 and 555 and a NAND2 gate in row 560.While the advantages of embodiments of the invention are present inother and more complex cells, two representative types of cells aredescribed in detail in table 500. For example, a four to one invertingmultiplexor that is 19 wire tracks wide in the 90 nm technology may bedesigned to occupy 18 tracks in a 65 nm technology with a 0.54 areascalar when the wire pitch of M2 lines is relaxed to the minimumcontacted gate pitch of 0.25 um.

The width of the cells for the inverters (rows 550 and 555) as well asthe NAND2 gate (row 560) for the 90 nm technology is listed in column510. The 90 nm technology describes cell arrangements without a fixed,polysilicon gate pitch. The wire pitch for the cells in the 90 nmtechnology is 0.28 um.

Columns 515 through 540 describe cell widths and area scalars for theinverters and the NAND2 gate for standard wiring and polysiliconarrangements (columns 515 and 520) and for two embodiments of thepresent invention in columns 525, 530, 535, and 540. Each embodiment inthe 65 nm technology restricts cell arrangements with a fixedpolysilicon gate pitch. For the 65 nm technology illustrated, theminimum contacted gate pitch is 0.25 um and the minimum wire pitch is0.20 um.

Columns 515 and 520 describe the width of the cells and area scalars forthe cells when the wire pitch for all metallization layers M2 through MXis set to the minimum wire pitch of 0.20 um and the gate pitch is set tothe minimum contacted gate pitch of 0.25 um. Note that the area scalarsfor this standard wiring arrangement are less than desired 50% areascalar. In particular, inverter row 550 indicates an area scalar of0.83, inverter row 555 indicates an area scalar of 0.83, and the NAND2gate row 560 indicates an area scalar of 0.63. Area scalars arecalculated by dividing the area of silicon occupied by the 65 nmtechnology cell by the area of silicon occupied by the 90 nm technologycell. For instance, the area for the inverter in row 550 is calculatedby multiplying the cell width of five tracks (column 515) by the M2 wirepitch of 0.20 um. This area is divided by the area of the 90 nmtechnology inverter, which is three tracks times the wire pitch of 0.28um. In each case, the height of the cell is assumed to scale by theratio of the 90 nm M3 pitch to the 65 nm M3 pitch.

Columns 525 and 530 describe the width of the cells and area scalars forthe cells when the wire pitch for metallization layer M2 equal to theminimum contacted device or gate pitch of 0.25 um and the gate pitch isset to the minimum contacted gate pitch of 0.25 um. Note that the areascalars for this embodiment are, on average, closer to the desired 50%area scalar. In particular, inverter row 550 indicates an area scalar of0.63, inverter row 555 indicates an area scalar of 0.42, and the NAND2gate row 560 indicates an area scalar of 0.47. In fact, the area scalarfor the inverter of row 555, which is 0.42, is unexpectedly smaller thanthe best technology scalar known while significantly improving the ACLVtolerance with the fixed gate pitch.

Columns 535 and 540 describe the width of the cells and area scalars forthe cells when the wire pitch for all metallization layers M2 through MXis set to the minimum wire pitch of 0.20 um and the gate pitch isrelaxed to reduce the lowest common multiple with the wire pitch. In thepresent embodiment, the gate pitch is relaxed 20% to 0.30 um to reducethe lowest common multiple to 0.60 um from the 1.0 um of the standardwiring arrangement in columns 515 and 520. Note that the area scalarsfor this embodiment are also, on average, closer to the desired 50% areascalar. In particular, inverter row 550 indicates an area scalar of0.50, inverter row 555 indicates an area scalar of 0.50, and the NAND2gate row 560 indicates an area scalar of 0.75.

FIG. 6 depicts a flowchart 600 of an embodiment to form an integratedcircuit with an adjusted metallization wire pitch for at least onemetallization layer. Flowchart begins with the definition of the minimumcontacted device or gate pitch to be employed with designing a libraryof cells for manufacturing the integrated circuit (element 610). Instandard cell designs, various cells that will be implemented in theintegrated circuit are designed to meet the constraints of thetechnology. In many embodiments, each cell in the standard library isdesigned to facilitate location of the cell next to any other cell alongan x-axis and/or y-axis on a silicon substrate. The only dimension thatvaries, in many embodiments, may be the width of the cell,advantageously allowing customization of the cells while allowing easeof placement.

Once the standard library is built, cells may be formed by a variety ofprocesses. For instance, through a series of masking, etching, and thelike, polysilicon gates may be formed on the surface of the substrate.Then, portions of the substrate may doped by ion implantation, to formn-wells and p-wells for NMOS and PMOS transistors. After polysilicon isformed to define the gate, drain and source regions, portions of thedrain and source regions may be further doped to form p+ and n+ regions.

Once the cell structures and gates are formed, a passivation layer suchas silicon oxide may be formed over the surface (element 625) prior toforming metallization layers to interconnect the cell structures. Toform the metallization layers, portions of the passivation layer may beetched away to form metal lines in a pre-determined pattern for themetallization layer (element 630).

After the surface of the substrate is prepared for the metal lines,metal is applied to the surface, filling in the etched lines andcovering the surface (element 635). The surface may then be planarizedto remove excess metal and another passivation layer is formed over themetal to separate the metal layer from other metal layers with anon-conductive material. This process of applying metallization layersmay be repeated until the metallization layer that is designated tocontact the input and output contacts for each cell (element 640). Insome embodiments, only metallization layer one may be formed up to thispoint. In further embodiments, additional layers such as metallizationlayers two and/or three may be formed.

Once reaching the metallization layer that is designated to contact theinput and output contacts for each cell, a subsequent metallizationlayer such as metallization layer M2 is formed with lines aligned abovethe centers of the polysilicon gates, having a pitch of the minimumcontacted device pitch (element 645). In some embodiments, more than onesuch metallization layer may be formed.

Additional metallization layers may then be formed that have a wirepitch equal to the minimum wire pitch or other pitch that is smallerthan the minimum device pitch (element 650). In other embodiments, morethan one metallization layers having a relaxed pitch may be formed atdifferent metallization layers such as metallization layers M2, M4,and/or M6.

FIG. 7 depicts a flowchart 700 of an embodiment to form an integratedcircuit with a relaxed polysilicon device pitch. Flowchart 700 beginswith determining a relaxed polysilicon gate pitch for standard cells(element 710). Designers may determine an advantageous relaxedpolysilicon gate pitch that reduces the lowest common multiple of thegate pitch and minimum wire pitch. In other embodiments, the selectedwire pitch may vary from the minimum wire pitch and the determination ofthe polysilicon gate pitch may take that wire pitch into account.

Upon determining the relaxed gate pitch, a standard cell library iscreated for manufacturing the integrated circuit (element 715). Furtherembodiments may incorporate more customized cells than a strict standardcell design. The cells are then created on a substrate with thepolysilicon gates pitched at the relaxed gate pitch (element 720).

After forming the cell structures and the polysilicon gates, apassivation layer is formed over the substrate (element 725). Portionsof the passivation layer may be removed via negative and/or positivephoto-resist masking and etching to provide poly contacts for the firstmetallization layer (element 730). Then, metallization layers are formedover the surface of the substrate with lines pitched at a minimum wirepitch to interconnect the cell structures and interconnect the cells(element 735).

Another embodiment of the invention is implemented as a program productfor use with a system to simulate and/or control semiconductormanufacturing integrated circuits in accordance with, e.g., flowchart600 and/or 700 as shown in FIGS. 6 and 7. The program(s) of the programproduct defines functions of the embodiments (including the methodsdescribed herein) and can be contained on a variety of data and/orsignal-bearing media. Illustrative data and/or signal-bearing mediainclude, but are not limited to: (i) information permanently stored onnon-writable storage media (e.g., read-only memory devices within acomputer such as CD-ROM disks readable by a CD-ROM drive); (ii)alterable information stored on writable storage media (e.g., floppydisks within a diskette drive or hard-disk drive); and (iii) informationconveyed to a computer by a communications medium, such as through acomputer or telephone network, including wireless communications. Thelatter embodiment specifically includes information downloaded from theInternet and other networks. Such data and/or signal-bearing media, whencarrying computer-readable instructions that direct the functions of thepresent invention, represent embodiments of the present invention.

In general, the routines executed to implement the embodiments of theinvention, may be part of an operating system or a specific application,component, program, module, object, or sequence of instructions. Thecomputer program of the present invention typically is comprised of amultitude of instructions that will be translated by a computer into amachine-readable format and hence executable instructions. Also,programs are comprised of variables and data structures that eitherreside locally to the program or are found in memory or on storagedevices. In addition, various programs described hereinafter may beidentified based upon the application for which they are implemented ina specific embodiment of the invention. However, it should beappreciated that any particular program nomenclature that follows isused merely for convenience, and thus the invention should not belimited to use solely in any specific application identified and/orimplied by such nomenclature.

It will be apparent to those skilled in the art having the benefit ofthis disclosure that the present invention contemplates methods andarrangements to interconnect cells and structures within cells formed ina semiconductor substrate of an integrated circuit to enhance celldensity. It is understood that the form of the invention shown anddescribed in the detailed description and the drawings are to be takenmerely as examples. It is intended that the following claims beinterpreted broadly to embrace all the variations of the exampleembodiments disclosed.

Although the present invention and some of its advantages have beendescribed in detail for some embodiments, it should be understood thatvarious changes, substitutions and alterations can be made hereinwithout departing from the spirit and scope of the invention as definedby the appended claims. Further, embodiments may achieve multipleobjectives but not every embodiment falling within the scope of theattached claims will achieve every objective. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

1. A method to form an integrated circuit constrained by a gate pitch,the method comprising: identifying the gate pitch of a substrate, thegate pitch being a distance between a centerline of a first gate and acenterline of a second gate that facilitates placement of a contactbetween the gates and in contact with a diffusion area of the substrate;forming cell structures with the substrate, wherein forming cellstructures with the substrate comprises forming gates in the substrateat the gate pitch and doping the substrate; forming a first set ofmetallization layers over the substrate to interconnect the cellstructures, the first set of metallization layers comprising lines, thelines being substantially parallel to the gates, wherein at least one ofthe first set is an adjusted metallization layer comprising adjustedlines, the adjusted lines being substantially parallel to the gates, theadjusted lines being pitched at the gate pitch and substantiallyvertically aligned with the gates, and, wherein at least another of thefirst set is an unadjusted metallization layer comprising lines pitchedat a first wire pitch, wherein the first wire pitch is different fromthe gate pitch, wherein the lines of the adjusted metallization layerconnect to the cell structures with contacts; and forming a second setof metallization layers over the substrate comprising lines, the linesbeing orthogonal to the gates, wherein the lines of the first set ofmetallization layers interconnect with the lines of the second set ofmetallization layers with vias to form circuitry of the integratedcircuit.
 2. The method of claim 1, further comprising forming at leasttwo vias to form connections with one or more of the adjusted lines atadjacent locations with respect to a wiring grid formed by the adjustedmetallization layer.
 3. The method of claim 1, further comprisingforming at least two vias to couple with the adjusted lines at adjacentwiring tracks of a wiring grid based upon the adjusted metallizationlayer, wherein the at least two vias are associated with at least twodissimilar nets.
 4. The method of claim 1, further comprising forming avia to couple with one of the adjusted lines at a contact that couples ametal layer one line with one of the gates or the diffusion area of thesubstrate, wherein the one of the adjusted lines is a metal layer twoline and the via interconnects the metal layer two line with the metallayer one line.
 5. The method of claim 4, wherein forming the viacomprises forming the via on a first adjusted wiring track, wherein asecond contact that interconnects another metal layer one line with oneof the gates or the diffusion area of the substrate for a dissimilar netis located at an adjacent intersection of an adjacent adjusted wiringtrack.
 6. The method of claim 4, wherein forming the via comprisesforming the via on a first adjusted wiring track, wherein a second viathat interconnects a second metal layer two line with a second metallayer one line for a dissimilar net is located at an adjacentintersection of an adjacent adjusted wiring track.
 7. The method ofclaim 1, wherein forming the first set of metallization layers comprisesinterconnecting the cell structures to form cells described in a libraryof cells.
 8. A method to form an integrated circuit constrained by agate pitch, the method comprising: identifying a relaxed gate pitch of asubstrate, the relaxed gate pitch being greater than a minimum distancebetween a centerline of a first gate and a centerline of a second gatethat facilitates placement of a contact between the first gate and thesecond gate to contact with a diffusion area of the substrate, whereinthe relaxed gate pitch has a common multiple with a wire pitch that issmaller than a lowest common multiple of the minimum distance and thewire pitch; forming cell structures with the substrate, wherein formingcell structures with the substrate comprises forming gates in thesubstrate at the relaxed gate pitch and doping the substrate; andforming a set of metallization layers over the substrate to interconnectthe cell structures, the set of metallization layers comprising lines,wherein at least one of the set is a metallization layer comprisinglines pitched at the wire pitch.
 9. The method of claim 8, whereinforming the set of metallization layers comprises forming the lineswithin at least one other layer pitched at a different wire pitch. 10.The method of claim 8, wherein forming the set of metallization layerscomprises forming the lines along pathways to interconnect cellstructures with other cell structures to implement logic functions. 11.The method of claim 8, wherein forming the set of metallization layerscomprises forming lines, which are substantially parallel with thegates, at a minimum wire pitch.